Solid-state image pickup device and signal reading method therefor

1. A solid-state image pickup device, comprising: one or more pixels, said or each pixel comprising: a photoelectric conversion part performing photoelectric conversion on incident light; a comparison part connected to an output terminal of the photoelectric conversion part to compare an output voltage of the photoelectric conversion part with a specified reference voltage and produce an output signal representing a result of the comparison; a reset part connected to the output terminal of the photoelectric conversion part to discharge a signal charge generated by the photoelectric conversion part; a capacitive element having two ends, one of which is connected to the output terminal of the photoelectric conversion part; and a control line connected to the other end of the capacitive element; and a control voltage application part applying a first control voltage to the control line during a signal storage period so as to make an electric potential at the output terminal of the photoelectric conversion part fall outside a transition region of the comparator, and applying a second control voltage to the control line during a signal read period so as to make the electric potential at the output terminal of the photoelectric conversion part fall within the transition region of the comparator.

2. The solid-state image pickup device as claimed in claim 1 , wherein the capacitive element comprises a MOSFET.

3. The solid-state image pickup device as claimed in claim 1 , wherein an electrode of the capacitive element is made of polysilicon.

4. The solid-state image pickup device as claimed in claim 1 , wherein an electrode of the capacitive element is made of metal.

5. The solid-state image pickup device as claimed in claim 1 , wherein the comparison part comprises an inverter circuit.

6. The solid-state image pickup device as claimed in claim 1 , wherein the pixels each have a row select switch which is connected to an output side of the associated comparison part, and the pixels are arrayed in a matrix form; the solid-state image pickup device further comprises a vertical scanner circuit selecting the pixels on a row-by-row basis; and the control line is a horizontal control line connected in common with a plurality of pixels of an identical row.

7. The solid-state image pickup device as claimed in claim 1 , further comprising a recording part for recording a time at which the output signal of the comparison part is inverted during the signal read period.

8. The solid-state image pickup device as claimed in claim 7 , wherein the recording part comprises a counter circuit and a latch circuit.

9. The solid-state image pickup device as claimed in claim 7 , wherein the pixels are arrayed in a matrix form, and recording parts are provided for each of columns of the pixels.

10. The solid-state image pickup device as claimed in claim 1 , wherein the reset part consists of a reset switch connected between an input terminal and an output terminal of the comparison part, the reset switch being turned ON to make the input terminal and the output terminal short-circuited so that an electric potential of the photoelectric conversion part is reset to a specified reset potential.

11. The solid-state image pickup device as claimed in claim 10 , wherein the reset switch comprises a MOSFET.

12. The solid-state image pickup device as claimed in claim 1 , further comprising a buffer part connected to an output terminal of the comparison part to receive the output signal of the comparison part and output a binary signal according to the received output signal.

13. The solid-state image pickup device as claimed in claim 1 , wherein the control voltage application part controls amplitude and a rate of change with time of the second control voltage to be applied to the control line.

14. The solid-state image pickup device as claimed in claim 1 , wherein the control voltage application part controls amplitude of the first control voltage and amplitude of the second control voltage in such a manner that a voltage for driving the photoelectric conversion part is limited.

15. A signal reading method for a solid-state image pickup device having a photoelectric conversion part performing photoelectric conversion on incident light, a comparison part connected to an output terminal of the photoelectric conversion part to compare an output voltage of the photoelectric conversion part with a specified reference voltage and produce an output signal representing a result of the comparison, a capacitive element one end of which is connected to the output terminal of the photoelectric conversion part, and a control line connected to the other end of the capacitive element, comprising: applying a first control voltage to the control line so as to make an electric potential at the output terminal of the photoelectric conversion part fall outside a transition region of the comparator during a signal storage period; and applying a second control voltage to the control line so as to make the electric potential at the output terminal of the photoelectric conversion part fall within the transition region of the comparator during a signal read period.